1. Technical Field
The present invention relates to a semiconductor device, and in particular to a semiconductor device containing an electrical fuse.
2. Related Art
There has conventionally been known a technique of preliminarily mounting a fuse to a semiconductor device, and disconnecting the fuse, in order to adjust resistivity of resistors used therein, or to disconnect an unacceptable element and replace it with a normal element.
Methods of disconnection of the fuse include a method of disconnecting the fuse by irradiating laser beam to a portion of the fuse, and a method of disconnecting the fuse with the aid of electric current.
U.S. Pat. No. 4,064,493, Japanese Laid-Open Patent Publication Nos. 2005-39220, 2005-57186 and 2006-253237 disclose electrical fuses disconnectable making use of a phenomenon such that a material composing the fuse moves based on electro-migration.
Japanese Laid-Open Patent Publication No. 2005-39220 discloses a fuse disconnectable with a smaller energy of current. In this publication, an electroconductive material composing the fuse is patterned while being folded a plurality of number of times. FIG. 12 is plan view showing the fuse disclosed in this publication. A fuse 1100 herein is folded twice.
The fuse 1100 has a current input terminal 1101, a current output terminal 1102, and between both terminals, a first forward straight portion 1103, a return straight portion 1104, and a second forward straight portion 1113. The fuse 1100 has also a first right-angled connection portion 1106 connecting the first forward straight portion 1103 and the return straight portion 1104, and a second right-angled connection portion 1107 connecting the second forward straight portion 1113 and the return straight portion 1104. When a predetermined current is allowed to flow from the current input terminal 1101 towards the current output terminal 1102 in thus-configured fuse 1100, heat generated in outer hatched portions 1108 of the fuse 1100 is summed up with heat generated in inner hatched portions 1109 of the fuse 1100, so that disconnection of the return straight portion 1104 fallen between the inner hatched portions 1109 is accelerated. The fuse 1100 may readily be disconnected in this way.
Japanese Laid-Open Patent Publication No. 2005-57186 describes a configuration in which lower and upper portions of a site of disconnection are covered with plates, and side portions are covered with vias. By virtue of this configuration, heat generated at the site of disconnection, when current is allowed to flow through the fuse, may successfully be confined or stored in the vicinity of the site of disconnection.
Japanese Laid-Open Patent Publication No. 2006-253237 describes a fuse element composed of a first interconnect, a second interconnect formed above the first interconnect while placing an insulating film in between, and a first via formed in the insulating film so as to connect the first interconnect and the second interconnect. The main portion of the first via is composed of a material more readily cause electro-migration than that composing the individual main portions of the first interconnect and the second interconnect. The publication also describes a configuration having a heater interconnect for heating the via provided therearound. This configuration reportedly allows elevation of temperature around the via in the process of disconnection, and is thereby capable of efficiently disconnecting the via.
The conventional configurations of the electrical fuse have, however, been anticipated for causing short-circuiting within the fuse, or between the fuse and the peripheral element thereof, in the process of disconnection of the fuse. In the technique disclosed in Japanese Laid-Open Patent Publication No. 2005-57186, the vias are formed on the lateral side of the interconnects, but the short-circuiting between the interconnects could not have been avoidable because of closely-adjacent arrangement of the ends of the interconnects composing the fuse. In the technique disclosed in Japanese Laid-Open Patent Publication No. 2006-253237, the heater interconnect is provided around the via portion, but the short-circuiting again could not have been avoidable when a material composing the interconnect is melt down, because there is no member protecting the interconnect formed therearound.
For the case where the fuse is disconnected making use of a phenomenon such that a material composing the fuse moves based on electro-migration as described in U.S. Pat. No. 4,064,493, Japanese Laid-Open Patent Publication Nos. 2005-39220, 2005-57186 and 2006-253237, any annealing given to the semiconductor device after disconnection of the fuse may cause re-movement of the material based on electro-migration, and thereby the site of disconnection may again recover connection. If such re-connection should occur, a target electrical fuse once supposedly be disconnected may not correctly be judged, in the process of inspecting whether the electrical fuse has been disconnected or not. This sort of disconnection might occur not so often, and is not supposed to raise a serious problem so far as the fuse is used under general operation, but it may be necessary to further improve performance of keeping a desirable state of disconnection, for the case where the semiconductor device is requested to ensure an extremely advanced level of reliability, or operated under severe conditions.